Endurance exercise is thought to reduce atherosclerotic risk through the alteration of plasma levels of low (LDL) and high (HDL) density lipoproteins. These lipoprotein fractions are polydisperse in humans and the subclasses are reputed to have differing atherogenicity. The Yucatan miniature pig (Sus scrofa), an animal which exhibits lipoprotein heterogeneity, will be used to determine whether chronic endurance exercise has an effect on lipoprotein subclass distribution. Subclass distribution will be determined using ultracentrifugation and gradient gel electrophoresis techniques. LDL and HDL concentrations will be correlated with the incidence and severity of atherosclerotic lesions in sedentary and exercise-trained swine.